Automated intravenous fluid regulating and administering apparatus

ABSTRACT

Automated dispensing apparatus is disclosed for administering intravenous fluid to a patient under gravity pressure at a controlled volumetric rate, such that deviations from a desired fluid volumetric rate are automatically corrected. The area and maximum width of each fluid drop are measured with two intersecting light beams. The light beams are either collimated or converging. Use of converging light beams is particularly advantageous when fogging or imperfections are present in the walls of a transparent tube through which the intravenous fluid flows. Apparatus, responsive to the light beams, generates signals representative of drop area and width, and these two parameters are combined to obtain a signal proportional to drop volume. The measured drop volume signal is compared with a rate control signal to automatically correct the fluid flow rate.

This application is a continuation-in-part application of Ser. No.202,412, filed Oct. 30, 1980.

This invention relates to medical electronics and, more specifically, toimproved intravenous flow regulation apparatus.

The intravenous administration of nutrients, electrolyte solution,and/or the like in the form of liquid dorps is a common practice,particularly for postoperative patients. Such a fluid delivery systemtypically is comprised of a source container, a drop chamber, tubing,and an administrating needle.

The introduction of fluids intravenously is commonly specified by thephysician in volumetric units, such as cc per hour. In practice,however, the actual flow rate of intravenous fluid may vary markedlyfrom the physician's specification, primarily as a result of thepatient's movements during intravenous feeding. Such patient movement islikely to retard the flow of intravenous fluid to the patient, or tocease the flow of intravenous fluid altogether in the event the needlebecomes obstructed. The patient's movements may also cause theintravenous fluid to flow too rapidly or at too great a rate such aswhen the patient changes position. In either event, the patient does notreceive the proper amount of nutrient or the like and, in extreme cases,this may result in the death of the patient.

In U.S. Pat. No. 4,111,198, a system is described for automaticallycontrolling the flow of intravenous fluid by maintaining the rate atwhich drops of fluid are applied to the patient per hour at a presetlevel. Thus, if the fluid is being applied at too great a rate, thatcondition is sensed and the tube flow resistance is automaticallyincreased, thereby decreasing the fluid flow rate. Conversely, when thefluid flow rate is sensed as being below the desired level, the tubeflow resistance is automatically reduced, thereby increasing the droprate to the desired value.

This system ensures administration of intravenous introduction of fluidsat the desired drop rate. However, for this system to be totallyeffective in achieving the desired volumetric control over the rate offluid introduction, the fluid drops must be normalized for variations indrop volume as the drop volume changes with rate of flow, time, and typeof fluid administered.

U.S. Pat. No. 4,173,224, a continuation-in-part application of U.S. Pat.No. 4,111,198, describes a system for determining the volume of eachdrop administered to a patient. As described in this patent the widthand silhouette of each fluid drop are measured and appropriate signalsgenerated which represent these two parameters. The signals are thenmultiplied to obtain a signal proportional to the volume of the drop andthis signal is combined with a rate control signal to reflect deviationsin the measured drop volume from a nominal value. Deviations from thenominal rate are used to adjust the actual rate of drop administration,ensuring that the fluid is supplied to the patient at the desiredvolumetric rate.

Although the system described in U.S. Pat. No. 4,173,224 greatlyimproves the intravenous administration of fluid over existing methods,it has been determined that certain techniques are helpful in furtherimproving the accuracy of this system.

It is therefore an object of the present invention to provide anintravenous fluid administering apparatus having a high degree ofaccuracy in controlling the volumetric fluid administration rate.

It is a further object of the present invention to provide an accurateintravenous fluid administering apparatus which is low in cost andreadily manufactured.

The above and other objects of the present invention are realized in anautomated intravenous fluid administration apparatus which regulates therate of fluid flow by the selective constriction of a fluid passingtube. A drop sensor circuit monitors the rate at which the fluid isbeing administered and also measures the volume of each drop.

In one embodiment drop volume is measured by apparatus including atleast two light sources, radiation emanating from each of said sourcesbeing directed along light paths perpendicular to each other, the lightpaths intersecting at a sensing point in a drop chamber through whicheach fluid drop passes. Associated circuitry detects the presence of adrop just prior to passing through the sensing point and also determinesthe maximum width of each drop. The drop chamber is advantageouslyconstructed with clear plastic walls coated with an anti-fogging agentor alternatively the walls are heated to prevent fogging that wouldreduce the accuracy of the volume measurements. The measured drop volumeper unit time is used to make necessary modifications to the fluid flowrate, thereby maintaining accurate and automatic control over thevolumetric rate of intravenous fluid flow to the patient.

In a second embodiment a multi-point LED array is used in place of thesingle LED light source. The LED array illuminates an opal glassdiffuser. A lens uses this source to produce a converging light beam inthe region of the fluid drop as it passes through the sensing point inthe drop chamber. This second embodiment improves measurement accuracywhen defects are present in the plastic walls of the drop chamber.

The above and other features and advantages of the present inventionwill become clear from the following detailed description of a specificillustrative embodiment thereof, presenting hereinbelow in conjunctionwith the accompanying drawings, in which:

FIGS. 1(A) and (B) are block diagrams of one embodiment of a drop volumemonitor in accordance with the instant invention;

FIG. 2(A) illustrates a first embodiment of an optical system utilizingtwo light sources for accurately determining drop volume when used inconjunction with the circuitry shown in FIGS. 1(A) and (B);

FIG. 2(B) illustrates a second embodiment of an optical system utilizinga converging light beam for accurately determining drop volume when usedin conjunction with the circuitry shown in FIGS. 1(A) and (B);

FIG. 3 is a timing diagram illustrating the operation of the circuitryin FIGS. 1(A) and 1(B);

FIG. 4 illustrates a drop chamber utilizing with the apparatus in FIGS.2(A) or 2(B), and

FIG. 5 illustrates apparatus for detecting the presence of a fluid dropprior to entering the drop chamber.

Referring now to FIGS. 1(A) and (B), there is schematically shown anautomated and regulated apparatus for intravenously injecting a fluid,such as an electrolyte solution, nutrients, or the like, into a patient,the volumetric or flow rate of administration being specified by thesetting of a panel control (not shown) allowing flow rates to be set inthe range of 1 to 99 milliliters/minute. The rate signal developed bythe panel control is applied to terminal 122 and from there to pulserate generator 121, the operation of which will be describedhereinafter.

The apparatus employs a bidirectionally operative motor 128, of the typedescribed in U.S. Pat. No. 4,173,224, which drives a clamping mechanism(not shown), as by a worm gear, to partially pinch off fluid-deliveringtubing to a proper degree such that the actual volumetric fluid flowrate to the patient is that specified by the panel control. To theextent that the actual flow rate, as measured in terms of the rate ofdrops per unit time, deviates from the specified rate, the apparatus, ina manner more fully discussed below, causes the motor to turn in adirection, and by an amount, to cause the proper fluid flow rate byvarying the inner delivery tube cross-sectional area, and thus its flowresistance. Thus, the motor is made to move in a direction either tounconstrict the tubing, i.e., create a larger inner cross-section toincrease the rate of fluid flow, if it is determined that the volumetricflow rate is less than the rate specified by the setting of the panelcontrol, or to pinch off the tube (reduce its inner cross-sectionalarea) if fluid is flowing at too high a rate, that is, greater than thedesired rate as established by the setting of the panel control.

FIG. 2(A) illustrates an optical system utilized in accordance with afirst embodiment of this invention. Light sources 201 and 200 are LightEmitting Diodes (LEDs) and are switched on alternately (as describedhereinafter) to measure the width and area of a fluid drop. LED 201 isutilized for the width measurement and LED 200 is used for the areameasurement. Light emanating from the light sources is selected to liealong perpendicular paths by apertures 203 and 204, and the pathsintersect at sensing point 202 through which each fluid drop passes.Light from LED 200 passes through sensing point 202, half silveredmirror 207, lens 208, aperture 209, a diffusion screen 210 and isapplied to Photodetector 211. Similarly light from sources 201 passesthrough sensing point 202, is reflected from mirrors 205, 206 and 207,passes through lens 208, aperture 209 and diffusion screen 210 and isalso applied to photodetector 211.

The arrangement of FIG. 2(A) differs from the arrangement shown in U.S.Pat. No. 4,173,224 in that two perpendicular light beams are used ratherthan one, and also the width (w) is measured in a plane perpendicular tothe projected area plane. Analysis has shown that the use of twoperpendicular light beams result in greater accuracy for volumemeasurements, particularly if the drop is tumbling.

In accordance with the teachings in U.S. Pat. No. 4,173,224 a drop offluid is approximately ellipsoidal in shape. The true volume of anellipsoid is equal to:

    Vt=(4/3)πwh.sup.2                                       (1)

where w is equal to drop width and h is equal to height. It has beendetermined that an accurate approximation of drop volume canalternatively be expressed by the relationship:

    V=(4/3)πWA=C.sub.v S.sub.w S.sub.A                      (2)

where w is the drop width in the X--Y plane, A is the drop area in theX--Z plane, S_(w) is a signal voltage proportional to drop width, S_(A)is a signal voltage proportional to drop area and C_(v) is a calibrationconstant. Apparatus to determine drop volume in accordance withexpression (2) and to control the fluid application rate will now bedescribed in detail.

Referring first to FIG. 4, there is illustrated a drop chamber throughwhich each fluid drop passes prior to administration to the patient. Thedrop chamber is attached, via tubing 400, to a standard bottle (notshown) containing the fluid to be administered to the patient. Fluidpasses out of the drop chamber via tubing 404. A drop formationapparatus 406 permits the fluid to be dispensed into the chamber onedrop at a time. The walls of the chamber at 405 are clear plastic, or,glass and are designed to permit the light beams emanating from thelight sources discussed above to pass through the chamber with a minimumof distortion. The passage of a light beam through the chamber isschematically illustrated in FIG. 4. It is, of course, understood thatthe sensing point 202 referred to in FIG. 2(A) lies in the path of thelight beams passing through the chamber.

To eliminate fogging of the drop chamber walls at 401, the walls arecoated with a wetting agent, such as Hydron. Fogging, of course,distorts the passage of the light beams and would reduce the accuracy ofthe measurement system. An alternative to the anti-fogging coating onthe chamber walls is an external heater (not shown), capable of heatingthe walls near the beam to a few degrees above ambient temperature whichalso eliminates fogging. Arranged beneath the light beam passage areabut above the fluid level at 403 is a splash suppressor 402, preferablycomprising a coarse wire mesh, designed to disperse the drop and thusreduce splashing onto the walls. In addition, the drop chamber issomewhat longer than normal to provide room for the passage of the lightbeam and proper function of the splash suppressor. Utilization of thesplash suppressor 402 prevents splash back onto the chamber walls whichcould also cause distortion of the light beam.

FIG. 2(B) illustrates one of the two illuminator detector packagesutilized in accordance with a second embodiment of this invention. Amultipoint LED array 212 replaces each of LEDs 200 and the two opticalsystems measure the respective width and area of the drop fromperpendicular directions. A multipoint LED array 212 replaces each ofLEDs 200 and 201 shown in FIG. 2(A). The LED array illuminates an opalglass diffuser 213 which is large enough to illuminate the desired areaof the drop chamber, the sidewalls of the drop chamber being shownschematically at 220. Lens 214 is positioned so that it can perform twoimaging requirements simultaneously. It images the diffuser ontocollecting lens 217 to maximize the effecient transfer of light. Itdefines the solid angle that drops (for example, drop 221) areilluminated with. This is done by aperture 215, since the center of thedrop chamber is one focal length (F1) from lens 214. Focal length F2 isthe focal length associated with lens 217. The extended diffuse sourceprovided by the opal glass diffuser 213 illuminates more than just asingle point at the center of the drop chamber. Lens 217 is used to forman image of the droplet on aperture 218. Aperture 218 is larger than thedrop and sets the maximum area of the beam. As discussed more fullybelow aperture 218 will be shaped like a slit if the width of the dropis being measured and shaped like a circle if the area of the drop isbeing measured. Behind aperture 218 is another diffuser 219 and aphotodetector 222. Aperture 216 is used to reject the light that isrefracted by the drop.

The embodiment shown in FIG. 2(B) differs from that shown in FIG. 2(A)in that a large diffuse light source is used to produce a convergingbeam instead of the collimated beam used in FIG. 2(A). When using aconverging beam, local defects at the drop chamber walls affect theentire illuminated region and will cause less perturbation in themeasurement of the droplet size. This is because any point in thevicinity of this fluid drop is illuminated by rays which pass throughmany points on the drop chamber wall. This optical system eliminates theneed for optical quality walls in the drop chamber and also eliminatesthe need for anti-fogging techniques.

Referring now to FIGS. 1(A) and 1(B) and considering the embodiment ofFIG. 2(A), the measurement sequence commences when a drop is releasedfrom drop apparatus 406 (FIG. 4). Before the drop passes the sensingpoint it is detected by capacitance detector 100 (describedhereinafter), resulting in the generation of ready signal R which isapplied to sequence control circuitry 101. Circuitry 101 generates anumber of sequence control signals (A-F) utilized in conjunction withthe circuitry in FIG. 1(B) with each signal generated being illustratedin FIG. 3. The details of sequence control circuit 101 are not given assuch details are apparent to one skilled in this art by reference to thewave forms shown in FIG. 3. Circuitry necessary to generate such waveforms can be found, for example, in "Pulse Digital And Switching WaveForm", by Millman and Taub, McGraw-Hill, 1966. The purpose of thecapacitance detector is to limit the electrical energy requirements ofthe system by controlling the time the LEDs are on.

Referring to FIG. 3, it is seen that after ready pulse R is generated,signal A drops to a low level, a width LED enable signal B is producedand immediately thereafter an area LED enable signal C is produced.Signal A dropping to a low level enables amplifier 106 in FIG. 1(A), theoutput of which was previously clamped to zero, to eliminate straybackground light effects. Signal B enables the width LED and the widthLED regulator circuit 107 and signal C enables the area LED and the areaLED regulator circuit 105. The function of regulator circuits 105 and107 is to automatically adjust the current supplied to the width andarea LEDs so that the base line of the photodetector 211 remainsconstant during the measurement process.

Subsequent to the generation of signal C width intensity amplifier 111is turned on by pulse D. The output of LED 201 is detected byphotodetector 211 and its output is in turn amplified by amplifier 106.The output of amplifier 106 is fed back to regulator 107 to maintain thewidth LED current at a constant level during the measurement process.The output of amplifier 106 is also applied to enabled width intensityamplifier 111, which is a track and hold amplifier designed to store asignal proportional to the width of the detected drop. The output signalfrom width intensity amplifier 111 is amplified by AC amplifier 110 andapplied to peak detector 114. Peat detector 114 produces a pulse P whenthe signal generated by width intensity amplifier 111 reaches a maximum.Due to the shape of the drop this signal maximum will occur when thedrop is in the center of the beam. Signal P, is used to briefly switchon width track and hold amplifier 113, causing this amplifier to storethe maximum width signal for later use. Signal P is also applied tosequence control 101 and in response thereto the sequence controlreturns signal D to its previous state and generates signal E. Signal Eis slightly delayed to permit the width track and hold amplifier 113time to store the width signal.

Subsequent to width LED 201 and width amplifier 111 being disabled bypulse D, the area intensity amplifier 108 is enabled by pulse E. Theoutput of the area LED is detected by photodetector 211, and its outputis in turn amplified by amplifier 106 and applied to area regulator 105to regulate the area LED current in the same manner regulator 107regulates the width LED output. The output signal from amplifier 106 isstored in area intensity amplifier 108, and the output of amplifier 108is in turn amplified by amplifier 109 and applied to area track and holdamplifier 115. Amplifier 115 is enabled by wave form E and stores thesignal representative of drop area for use at a later time. At this timetherefore signal voltages proportional to drop width (S_(w)) and droparea (S_(a)) have been obtained and stored in amplifiers 113 and 115,respectively. The signal voltages are shown at line X in FIG. 3.

To determine drop volume in accordance with expression (2); it isnecessary to obtain a digital signal proportional to the product ofanalog signals S_(w) and S_(a). This is accomplished with a circuitwhich combines analog-to-digital conversion (single ramp method), andthe product function. More particularly, voltage to frequency converter116 produces a pulse train with a frequency F_(a) proportional to thearea signal stored in amplifier 115. A ramp signal (line Y, FIG. 3) isgenerated by voltage to pulse width converter 112 with the generation ofthe ramp being initiated by the trailing edge of timing signal E.Converter 112 produces a counter gate pulse T_(w) when the width signalvoltage, S_(w), stored in amplifier 113 is greater than the rampvoltage. This relationship is illustrated at lines Y and F in FIG. 3.Therefore the pulse duration of signal T_(w) is proportional to the dropwidth. Gate 117 allows the area frequency signal F_(a) to pass only whenenabled by pulse T_(w). The pulses passed through gate 117 are stored incounter 218 and the number of pulses for each drop is determined by thefollowing relationship:

    N.sub.f =T.sub.w F.sub.a =KWA

where K is a calibration constant.

Several gain or conversion factors would effect the calibrationconstant, such as the slope of the ramp generator. However once thecalibration constant is set for a particular instrument it shouldinfrequently or never require recalibration if quality components areused.

It is necessary that frequency F_(a) be high enough to ensure that thecount stored in counter 118 has the required resolution, preferablygreater than 100 for 1% accuracy. Counter 118 performs a prescalingfunction so that the number of pulses at the output of counter 118 isnumerically equal to the volume in milliliters or tenths of milliliters.The output of counter 118 is applied to four digit decade counter 119and four digit display 123. The count is accumulated in counter 119 anddisplay 123 records drop volume directly in milliliters.

The output of counter 118 is also applied to up/down counter 120. Theup/down counter counts up in response to the output of counter 118 andcounts down in response to the output of pulse rate generator 121. Theoutput frequency of the pulse rate generator is set by a panel control(not shown) which applies a frequency control signal to terminal 122.The panel control permits the desired rate of application to be set inthe range of 1 to 99 milliliters per minute. Pulse rate generator 121generates a pulse train having a frequency proportional to the settingon the panel control.

The count stored in counter 120 determines the operation of motor 128.More particularly, if the count is close to zero motor driver 124 isdisabled and motor 128 remains off. Therefore the clamping mechanismassociated with the motor (described above) maintains its presetposition, thereby maintaining a preset flow rate through the tubefeeding the drop chamber. If the net count in counter 120 differs fromzero by a predetermined amount after a certain interval, (e.g., everyeight drops or equivalent period), a trigger signal is applied to oneshot (monostable multivibrator) 125. The signal generated by one shot125 is applied to motor driver 124 and will operate the motor for aperiod proportional to the width of the pulse generated by the one shot.If the count is positive the motor closes the clamping mechanism. If thecount is negative a reverse signal is applied to motor driver 124, themotor direction is reversed, and the clamp is opened.

Pulse width of the output of the one shot is determined by photodetector127 and amplifier 126. More particularly, an optical assembly (notshown) generates a light beam with an intensity proportional to the flowrate and the light beam is focused on photodetector 127. The outputsignal from photodetector 127 is therefore proportional to the clampdisplacement and thus the flow rate. The photodetector output signal isapplied to amplifier 126, which in turn generates a signal to controlthe width of the output pulse of one shot 125. In this manner thereforethe period of operation for motor 128 is determined by the clampposition. The objective of this arrangement is to avoid overshoot and toobtain proper flow control over a period of seconds rather than minutes.If left on continuously the motor operates the clamp from full open tofull close in approximately 10 to 30 seconds. Added features (not shown)are to detect large counter values, increase motor speed proportionally,and to sound an alarm indicating an undesirable large deviation betweendesired and actual delivered volume.

When utilizing the embodiment of FIG. 2(B) in place of the embodiment ofFIG. 2(A), two separate orthogonal optical systems, one for widthmeasurements and one for area measurements, are required rather than thesingle optical system shown in FIG. 2(A). For area measurements aperture219 will be shaped like a circle and for width measurement aperture 219will be shaped like a slit. Enable signals B and C discussed above willalternately enable each LED array and its associated photodetector toperform the area and width measurements. The remaining circuitry shownin FIGS. 1(A) and 1(B) operates in the same manner described above whenused in conjunction with the embodiment shown in FIG. 2(B).

Referring now to FIG. 5, there is shown the capacitive detector 100previously described. When a drop from drop apparatus 500 passeselectrodes 502 in body 501, their capacitance changes and a frequencyshift occurs in the output of oscillator 503. The shift in frequency isdetected by frequency to voltage converter 504 and in response theretoan AC output pulse is produced. This pulse is shaped by pulse shaper 505and used as the ready signal described above.

The above described arrangement is merely illustrative of the principalsof the present invention and numerous modifications and adaptionsthereof will be readily apparent to those skilled in the art withoutdeparting from the spirit and scope of the present invention.

What is claimed is:
 1. An intravenous fluid regulator apparatuscomprising:means for generating a first signal representing a desiredrate of introduction of drops of intravenous fluid to a patient, meansfor sensing the volume of each of said drops of fluid, said sensingmeans including at least two diffuse light sources arranged to produceconverging light beams, radiation from each of said converging lightbeams being selected to lie along light paths perpendicular to eachother, said light paths intersecting at a sensing point through whicheach fluid drop passes, means responsive to said sensing means forgenerating a second signal bearing a relation to drop volume, and foroperatively combining said first and second signals to produce a fluidintroduction rate control signal.
 2. An intravenous fluid regulatorapparatus in accordance with claim 1, wherein there is further includedmeans for detecting a fluid drop prior to the time said fluid droppasses through said sensing point and means responsive to said detectingmeans for enabling said sensing means.
 3. An intravenous fluid regulatorin accordance with claim 2, wherein there is further included means fordetermining the maximum width of said fluid drop as it passes throughsaid sensing point.
 4. An intravenous fluid regulator in accordance withclaim 3, wherein said sensing means further includes means responsive toone of said light sources for producing a signal proportional to thearea of a fluid drop, means responsive to the other of said lightsources for producing a signal proportional to the maximum width of saidfluid drop and means for operatively combining said proportional areasignal and said proportional width signal to produce said second signal.5. An intravenous fluid regulator in accordance with claim 4, whereinsaid first and second signal combining means include means foraccumulating a count signal in response to said second signal, means fordecreasing said accumulated count signal in response to said firstsignal and means for varying said fluid introduction rate control signalin response to the magnitude of said accumulated count signal.
 6. Anintravenous fluid regulator in accordance with claim 1, wherein each ofsaid diffuse light sources includes an LED array arranged to illuminatea first glass diffuser, light emanating from said first glass diffuserbeing directed through first and second lenses on to a photodetector. 7.An intravenous fluid regulator in accordance with claim 6, wherein saidsensing point lies within a drop chamber, said drop chamber beingpositioned between said first and second lenses, being cylindrical inshape and having a top aperture to admit said fluid drops, and a bottomaperture to exit said fluid drops.
 8. An intravenous fluid regulator inaccordance with claim 7, wherein the center of said drop chamber ispositioned at a distance from said first lens equal to one first lensfocal length and at a distance from said second lens equal to two secondlens focal lengths.
 9. An intravenous fluid regulator in accordance withclaim 6, wherein each of said diffuse light sources further includes asecond glass diffuser positioned between said photodetector and saidsecond lens.
 10. An intravenous fluid regulator in accordance with claim9, wherein each of said diffuse light sources further include first andsecond apertures positioned between said first and second lenses and athird aperture positioned between said second lens and said second glassdiffuser.